Radio beacon



m 1947' I A. ALl-f oRo ETAL. V 2,414,431

RADIO BEACON Filed July 1 1942 3 Sheets-Sheet 1 l/O/CE 23 SOURCE INVENTORS AND/em xlzfow BY y J Mme/14w ATI'ONY Patented Jan. 21, 1947 RADIO BEACON Andrew Alford and Nathan Marchand, New York, N. Y., assignors to Federal Telephone and Radio Corporation, a corporation of Delaware Application July 1, 1942, Serial No. 449,258

17 Claims.

1 Thisinvention relates to radio transmitter systems and more particularly to radio beacons.

In a copending application of Andrew Alford,

' Serial No. 445,944, filed June 5, 1942, entitled Multisignal radiating system there is disclosed a system in which signals are directively radiated to define a course line while at the same time and on the same wavelength further signals such as voice signals are transmitted. Alternatively, according to this copending application, a system isproposed wherein a four-course beacon utilizing a common transmitting antennaiis provided. According to this previously proposed system the voice and signals or the signals for defining two courses are combined by means of a transmission line bridge arrangement so constructed that only side band energy need be dissipated without necessitating dissipation of half. the carrier frequency energy as is required in most hybrid coil or balancing network systems. This previous arrangement, however, does require a dissipating network coupled tothe balancing bridge in order to assure operation without interference between the voicesignals and the course signals.

Further in another copending application of Andrew Alford, Serial No. 381,301, filed March 1, 1941, entitled Electronic beacon modulator is disclosed a system in which two visual course identifyingsignals are used to electronically modulate a carrier frequency. This modulated carrier is then applied over a high frequency bridge to antenna units to produce the desired course beacon. The weakening of either of the modulators, or a phase shift therein will not cause any shift in the course but willresult in a broadem'ng of the course.

It is an object of our invention to provide for the simultaneoustransmission of voice and course indicating signals without the necessity of providing balanced bridge circuits with dissipating resistance networks.

"Itis a further object of our invention to provide a system permittingfour-courseor sector identification beacon systems to be used together with voice signal energy at the same carrier frequency.

It is a still further object of our invention touprovide a radio beacon arrangement in. which the signals of voice frequency may be applied through vacuum tube modulators to the antenna units while at the same time course identification signals are applied to these antenna units without endangering the beacon course indications either by causing a shiftof the course or a broadeningrof the course line.

ltisa further objectof our invention to provide a radio beacon using electronic modulation in which the low frequency components defining the visual beacon course may be applied directly to the antenna units of a radio beacon without requiring a separate combining bridge network ahead of the modulator.

According toone feature of our invention, there are provided two separate modulators which are partially modulated by voice signal energy, and to one or more of these modulators is supplied a course identifying signal. The modulated carrier is. applied to a combining system so that in one part the voice and carrier frequencies balance out in opposed phase leaving only the course identifyingsignal which is applied to a course defining antenna system and at a separate output of the combining circuit the modulator outputs combine in additive phase relationship and are applied to otherantenna units to supply the beacon carrier on-course indications and the voice modulated energy.

According to another feature of our invention two course identifying signalsin a given phase relation may be applied to one modulator, and the same course identifying signals in phase quadrature may be applied to a second modulator, the side-band energy from said one modulator being applied to a pair of spaced antenna units and that of said second modulator being applied to a central antenna unit, the carrier frequency also being applied to the central antenna. In this circuit theelectrical length of the antenna feed lines from both modulators should be such as to avoid the usual phase shift of this system. Voice signals may also be applied so as to feed the central antenna unit if desired.

A better understanding of our invention and the objects and features thereof may be had from the particular description thereof made with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic illustration of a radio beacon in accordance with our invention;

Fig. 1A is a simplified beacon similar to that of Fig. 1;

Fig. 2 is a modified circuit which may be substituted for part of the circuit shown in Fig. 1;

Fig. 3 is a further modification which maybe substituted for part of the circuit shown in Fig. 2; and

Fig. 3A is a furthermodification and simplification of the beacon.

In Fig. 1 three antenna elements I, 2 and 3 are shownhorizontally disposed in 'a substantially straight line, elements. I and 3 being interconnected by transmission line 4 provided with a transposition 5 and substantially equally spaced from central antenna 2. Two other antenna units 1 and 9 are shown substantially equally spaced on either side of antenna 2 and interconnected by transmission line 8 provided with a transposition I0. Preferably, these antenna units are horizontal loops of the type more fully described in U. S. Patent No. 2,283,897, issued on May 26, 1942. It should be understood, however, that the principles of our invention apply equally well to radio systems utilizing other types of antennae such as dipoles or the like. In place of antennae I, 2 and 3 as well as? and 9, if desired, suitably arranged arrays may be used. However, since the particular nature of the antenna units used is of no material concern the most simple arrangement is shown.

For simplification of the description the circuit arrangement of the antenna units I. 2 and 3 for providing a single course beacon will first be separately described. This unit is shown in a more simplified form in Fig. 1A wherein the same reference characters are used to refer to corresponding D rts. From radio frequency source 20 radio frequency energy is supplied to modulators 2| and 22. These modulators may beof any desired type, for example, they may be vacuum tube modulators; To modulators 2| and 22 voice signals or any other desired information conveying signals may be applied from source 23. These voice signals are of such an amplitude as to only partially modulate the radio frequency energy in 2|-22. For example, the voice signals may be such as to 40% modulate this radio frequency energy. From a separate source 24 is applied a course identifying signal which in the case of keyed aural signals may be an audio frequency such as 1020 cycles. This signal is of sufficient amplitude to complete the modulation in modulator 22 to 100%. Thus, if the voice signals only 40% modulate the signals then the course identification signals may modulate the carrier 60%.

The outputs of modulators 2I22 are brought to the opposite diagonals of the hybrid bridge network or transmission line bridge 25. This bridge is preferably of the type disclosed in U. S. Patent No. 2,147,809. A transposition 2B is provided in one arm of the bridge. The energy then applied at the opposite diagonals combine in phase at the upper diagonal 21 of the bridge so that at this point there is an output of the carrier frequency and modulation side bands of both the voice frequency signals and the course identifying signals. These output signals are applied to antenna 2.' At the lower corner of bridge 25 the carrier frequency and voice frequency signals combine in phase opposition leaving only side bands of the carrier modulated with the course identifying signals. These signals are applied over a reversing switch 29 to the antenna units I and 3. The transmission lines coupling bridge 25 to antenna 2 and to antennae I and 3 should be such that the carrier-course identifying side bands in antenna 2 are related 90 in phase with the carrier in antenna elements land 3. This may easily be accomplished by making the lines differ in length by a quarter wavelength. In order to provide the beacon indications a relay 3|] is provided and operated by a keyer 3| so that reversing switch 29 is operated to periodically reverse the phase of energy supplied to' antennae I and 3.with respect to the energy. supplied tofzantenna 2.

It will thus be seen that with the circuit so far described, a two-course keyed beacon is provided and at the same time voice frequency signals of the same carrier frequency are applied to central antenna 2. Likewise, it can be seen that if either of the modulators 2| or 22 becomes weakened with respect to the other no effect on the radio beacon course indicationwill occur. The unbalance between modulators 2| and 2 will merely serve to feed some of the carrier frequency energy and some of the voice side bands to antennae I and 3 but will not serve to shift the course or broaden it in any way.

In the event a further course at right angles to that producedby antenna units I, 2 and 3 is desired this may be accomplished by the additional apparatus described below and illustrated.

in Fig. 1. Energy from the source 20 is supplied over a bridge network 32 to a second bridge network 33 similar to network 25. It should be noted that in the case of bridge network'32 a balancing or dissipating network .34 is necessary. In the lines connected to the opposite diagonals of bridge 32 are provided modulating elements 35, 35 which may be of any known form and merely serve to impart to the carrier frequency in the separate lines different distinctive signal indications, for example, 90 and 150 cycle signals. The two modulators 35, 36 are preferably driven by a common drive motor 31 although any synchronized drive means may be used. The carrier frequency modulated with the 90 and 150 cycle energy is balanced out at the lower diagonal point of bridge 33 and the side bands applied to antenna units 1 and 9 to produce the course inclication pattern. At the upper point of bridge 33 the carrier and modulation side bands combine in phase and are applied over a further bridge 10 to central antenna 2. Bridge 40 is used when the additional signals are to be applied to antenna 2 for maintaining balance between the energy supplied from bridge 25 and from bridge 33. Bridge is similar to bridge 32 and the principles thereof are morefully discussed in the previously mentioned Alford application, Serial No. 445,944. By the use of this network energy is supplied to central antenna 2' from the two sources. However, the carrier frequency energy from the two sources balances out at the lower terminal of bridge 40 so that network 4| need dissipate only the side band energy from these two sources.

It will be seen that in the complete system of v Fig. 1 the central antenna element 2 carries three different and independent signal components, namely the voice signals, the course identifying signals from source 24 and the beacon signals from modulators 35, 36. However, the arrangement is such that all of these signals may be carried in the same central antenna which at the same time is usedin cooperation with antennae I and 3 to define one course and with antennae I and 9 to define a second course.

In Fig. 2 is illustrated a further modification of our invention which may be used in place of that part of the beacon circuit of Fig. 1 shown below the line 2-2 of Fig. 1. The arrangement of Fig. 2 permits the application of two signals, such as voice signals and course identifying signalsQto sets of antennae such as I, 2 and 3 of Figs. 1 or 1A while permitting full use of the modulation capacity of the modulators 5| and 52. According to this system the course identifying source 24 is coupled over coil 53 to modulators 5l and 52 in such a manner that the energy from this source is applied in phase opposition to the two modue lators. 24 is applied through a suitable phase shifter 54 to coil 55 from which coil it is applied in parallel or like phase to each of the modulators and 52. The phase shifter 54 is provided to se- Cure the desired phase relationship between the energy supplied from source 24 over coils 53 and 55. For best operation of the system the phase shifter should be such that a 90 phase relation is maintained between the energy supplied at the two coils. At the same time voice signals or other desired information signals may be applied to the line coupled to coil 55. Carrier frequency energy from source 26] is also applied to the modulators.

Since the course identifying energy supplied over coil 55 to the modulators is in phase oppo siticn, it is clear that the side-bands from modulators 5E, 52 derived therefrom will arrive at point 21 in phase opposition while the energy supplied to the modulators from coil 55, that is, the voice frequency and part of the course identifying signal will arrive at point 2'! of bridge 25 in additive phase relationship. Similarly, the energy supplied over coil 53 will arrive at the lower terminal of bridge 25 in additive phase relationship for application to antennae l and 3 while the course identifying signals from coil 55, the voice signals and carrier frequency energy will all balance out. It cantherefore be seen that the length of line interconnecting terminal 21 of bridge 25 and antenna 2 and the line connecting the lower terminal of bridge 25 and antennae l and 3 should be of equal length since the desired phase quadrature relationship of the energy is obtained by means of phase shifter 55. It should further be noted that every one of the signals employed is applied to each of the modulators 5|, 52 in this case so that the full capacity of both modulators may be employed.

While we have illustrated herein the transversal of bridge 25 in one of the lower arms, it is clear that this transposition could be made in one of the upper arms of the bridge if desired. In this case the course indication and voice frequency signals should be applied at coil 53 instead of coil 55 so that they will add in the proper phase relationship for feeding the central antenna and the pure course indication signals should then be applied at coil 55 for proper energization of the outer antenna units.

It is also to be noted that the system of Fig. 2 combined with Figs. 1 or 1A may be used as a single two-course beacon by omitting antenna units 1 and 9 of Fig. 1 and the circuit elements pertinent thereto. This avoids the necessity of a bridge such as bridge-40 of Fig. l and the additional modulating equipment. However, it is clear that the arrangement of Fig. 2 may likewise be combined with the second course beacon as shown in Fig. 1.

The modulating arrangement of Fig. 2 may also be readily applied to distinctive signal visual beacon arrangements instead of the keyed aural beacon system illustrated. The arrangement of Fig. 3 may be used to replace the parts of the circuit of Fig. 2 connected as indicated by lines 3-3 and 3a-3a. In this arrangement is shown a motor 69 driving two alternators El and 62. While two separate alternators are shown for simplification of illustration, it is clear that a combined unit for producing the two tone or visual indicating frequencies could be used. Furthermore, any two sources of constant amplitude energylmay be used in place of the alternators At the same time energy from source shown. For example, tuning fork controlled sources may be used. The output of the two alternators BI, 62 is applied to conjugate points of a hybrid coil network or other audio frequency bridge 63. Thus, the energy at one terminal of bridge 63 will apply as one of the distinctive frequencies, for example, the cycle frequency in opposite phase to that at the opposite terminal of the bridge while the other frequency, for example, the cycle frequency will be in phase with the component at the first named terminal of the bridge. The two in phase components may be applied over phase shifter 54 to the coil 55 of Fig. 2. If voice frequency is to be applied at the same time, a balancing bridge or hybrid coil circuit 64 is necessary, the voice signals from voice source 23 being applied at one terminal of the bridge while the Bil-I50 cycle signals are applied to the corresponding conjugate terminal of the bridge. A dissipating network 55 is necessary in order to maintain the balance of the bridge, this network 65 being connected at the terminal opposite that at which phase shifter 55 is applied. This network 65 will dissipate half of the voice signals and visual signals applied to the bridge but since these signals may be readily obtained, this does not clearly detract from the efficiency of the system as a whole.

The phase shifter should be of a type such that both the 90 and 150 cycle energies are shifted the same amount with respect to the energy fed to the alternators over coil 53. One suitable form of phase shift may be accomplished by modulating a sub carrier with the signals shifting the phase of this carrier and then demodulating the carrier to derive the phase shifted modulating signals. Instead of providing a phase shifter separately generated signals in phase quadrature may be supplied. This merely requires that each generator be provided with two rotors offset to produce the low frequency signals in phase quadrature. Then two separate sources for each of these 90 and 150 cycle energies will be provided. Amplitude equality of the two signals may be acquired by proper design of the alternators.

The voice signals and the beacon visual signals are thus applied over coil 55 to modulators 5|, 52 of Fig. 2. At the same time the visual course signals are applied through an attenuator 66 to coil 53 of modulators 5|, 52. Attenuator 65 is required to bring the signals applied to coil 53 down to the same level as those applied to coil 55 and is necessitated because of the dissipation of signal energy in network 65.

The voice signals and the 90 and 150 cycle energy may be applied at low levels since any R. F. phase shift or difierence in amplitude at the output of the modulators will not shift the course, and consequently amplification may precede or follow modulation. Thus, the energy dissipated may be kept very low.

It will be seen that with this arrangement the proper phase relationship of the 90-150 cycle modulated energy for application to this antennae is obtained by the transposition in bridge 25 of Fig. 2. Thus, when the modulated signals are applied through the circuit of Fig. 2 to antenna units 2 and 3 of Fig. 1 or 1A, they will be in the proper phase relationhip to produce the desired course. It is further to be noted that this arrangement may also be used in combination with the visual system utilizing antenna 1, 2' and 9 of Fig. 1 if desired. In this case, however, the-visual indicating frequencies of modulators 35 and 36 should be different from those produced in alternators 6| and 62 in order that confusion between the courses may not result. It is also to be understood that if desired a keying arrangement may be used for the second antenna system I, 2 and 9 similar to that disclosed in Fig. 1 for the beacon I, 2 and 3. in place of the visual modulator shown.

Although we have described this last form of our invention as applicable to the particular modification shown in Fig. 2, it should be understood that this form of our invention is adaptable to a much simpler construction. The separately provided course determining signals, for example 90 and 150 cycle signals, may be derived by any means such as that shown in Fig. 3 or by separate generators as shown in Fig. 3A, so that say a first set of 90 and 150 cycle signals from MA are produced in a particular phase relationship and a second set of 90 and 150 cycle signals from 62A are in phase quadrature therewith, but with one of these second signals leading in phase and the other lagging in phase with respect to the corresponding signal of the first set. This modification can be more readily understood by reference to Fig. 3A replacing the portion of Fig. 1A below line 3a-3a.

The energy from 61A may then be fed directly to modulator 2IA and from 62A directly to modulator 22A. With this arrangement the coils 53 and 55 of Fig. 2 may be omitted. The outputs from modulators 2IA and 22'A have envelopes with the phase quadrature relationship required. This modulated energy is then supplied to a bridge such as 25 of Fig. 1A and to the antenna units l, 2 and 3 to produce the beacon course. In this construction the feed lines for both antenna systems should be the same length as phase shifts are not desirable.

A diiference in amplitude of energy from modulators 2|A and 22A will cause a feed of some of the energy from each transmitter to both antennae systems disturbing the phase quadrature relationship of the combined envelopes in both antennae systems. This will have the effect of making the course signal weaker but will not cause any shifting of the course.

A phase shift in either modulator will rotate the carrier and sidebands of either as a whole producing unequal upper and lower sidebands. This effect constitutes second harmonic distortion but beyond a slight weakening of the course will not produce any charge therein. The second harmonic distortion may be objectionable from a standpoint of interference with voice signals, and in general is not desired. The beacon may be readily monitored for this condition however by providing at the monitoring station a system for indicating the presence of a second harmonic as well as the usual course indicating arrangement. This is a convenient way of checking phase.

If it is desired to transmit voice signals as well as the course indicating signals these voice signals may be readily applied to modulators 2 IA and MA by any desired means. It is merely necessary that the voice signals and course indicating signals do not over-modulate the carrier.

One additional advantage of the system described in connection with Figs. 2, 3 and 3A is that no phase shift is required in the lines feeding the carrier to the antenna units. Consequently, the beacon may be used without modification at different carrier frequencies. The sharpness of the course produced will, of course,

vary with the carrier frequency, but the phase quadrature relationship of the envelope frequencies will be preserved.

While in the description of our invention in connection with Fig. 1, mechanical modulators have been shown, it is clear that if desired electronic modulation such as shown in said application, Serial No. 381,301, or other forms of modulation may be used if desired. Moreover, the principles described with reference to Fig. 3A may be applied to tone modulation with keying if desired as well as to the beacons defined by two distinctive tone signals.

With the beacon system in accordance with our invention voice signals may be readily applied to any known beacon arrangements without requiring an additional carrier frequency. For this reason reception of the signals on an aircraft is greatly simplified. All of the signals may be received in a common radio frequency amplifier and separated by audio frequency filters after detection. Furthermore, no phase shift at radio frequency is required in several embodiments of the invention.

While we have disclosed only a limited number of embodiments of our invention, it should be distinctly understood that these are given merely by way of illustration and are not intended to define the scope of our invention. Many modifications thereof will occur to those skilled in the art within the scope of our invention as embodied in the accompanying claims.

What is claimed is:

1. A radio transmitting system comprising a first antenna system, a second antenna system, a pair of modulators, a first source of signals, a second source of signals, a carrier frequency source, means for applying energy from said first signal source and said carrier frequency source to both said modulators, means for applying energy from said second signal source to at least one of said modulators, first means for combining modulated energy from said two modulators to suppress the carrier frequency and said first signal and applying the resultant energy to said first antenna system, second means for combining modulated energy from said two modulators to maintain the carrier frequency and said first signal and applying the resultant to said second antenna system.

2. A radio transmitting system according to claim 1 wherein said first antenna system comprises two spaced antenna units coupled together in phase opposition, and said second antenna system comprises an antenna unit arranged substantially symmetrically between said two spaced antenna units.

3. A radio transmitting system according to claim 1 wherein said first signal source is a source of voice signals and said second signal source is a source of course identifying signals.

4. A radio transmitter according to claim 1 wherein said first source of signals comprises a source of two distinctive signals combined in a first manner and said second source of signals comprises a source of said two distinctive signals combined in a different second manner such that one of said distinctive signals is reversed in phase with respect to the corresponding distinctive signal in said first source.

5. A radio beacon for simultaneous transmission of voice and guide signals comprising a first antenna system, a second antenna system, first and second modulators, means for supplying carrier frequency energy and voice signals to said modulators, means for supplying a course identie 9 fying frequency to at least 'one of said modulators, first combining means for combining the modulated output of said modulators with the carrier frequency energy and the voice signal energy from said first and second modulators in phase opposition, first coupling means for coupling said first combiningmeans to said first antenna system to radiate only sideband energy of said' course identifying frequency, a second combining means for combining the output of said modulators with the carrier frequency energy and the voice signal energy from said modulators inphase with one another, and second coupling means for coupling the output of said second combining means to said second antenna system to radiate carrier frequency energy and sidebandenergy of said voice signals and said course identifying frequency, to complete the radiation pattern for said beacon and to transmit desired voice signals.

6. A radio beacon system according to claim further comprising keying means for alternately reversing the phase of energy supplied to said first antenna means with respect to that supplied to said second antenna means.

7. A radio beacon for simultaneous transmission of voice and guide signals comprising a first antenna system including two antennae coupled together in phase opposition, a second antenna system including an antenna substantially symmetrically arranged between said two antennae, first and second modulators, means for supplying carrier frequency energy and voice signals to said modulators, means for supplying a course identifying frequency signal to at least one of said modulators, first combining means for combining the modulated output of said modulators with the carrier frequency energy and the voice signal energy from said first and second modulators in phase opposition, first coupling means for coupling said first combining means to said first antenna system to radiate only side band energy of said course identifying frequency, a second combining means for combining the output of said modulators with the carrier frequency energy and the voice signal energy from said modulators in phase with one another, and second coupling means for coupling the output of said second combining means to said second antenna system to radiate carrier frequency energy and sideband energy of said voice signals and said course identifying frequency, to complete the radiation pattern for said beacon and to transmit desired voice signals.

8. A radio beacon according to claim '7 wherein said voicesignals are applied to only partially modulate the carrier energy applied to said modulators, and said course identifying signal is applied to only one of said modulators to further modulate it in combination with said applied voice signal,

9. A radio beacon according to claim '7 wherein said voice signals are applied to only partially modulate the carrier energy applied to said modulators, and said course identifying signal is applied to both modulators in different phase relation to further modulate the carrier energy applied to said modulators in combination with said voice signals.

10. A radio beacon according to claim 7 wherein said course identifying signal comprises two distinctive signal frequencies 11. A radio beacon according to claim '7 further comprising a third antenna system including two antennae spaced on either side of said second antenna and in a line substantially at right angles to the antenna of said first antenna system, the antennae of said third system being coupled together in phase opposition, a third modulator means for separately modulating energy of said carrier frequency with two distinctive signals, means for combining said separately modulated energy with the carriers in additive phase relation and applying energy so combined to said second antenna system, and means for combining said separately modulated energy with the carriers in phase opposition and applying the energy so combined to said third antenna system.

12. A radio beacon comprising a first antenna system comprising a pair of spaced radiating means, a second antenna system comprising a centrally arranged radiating means, a pair of modulators, a first source of two course indicating signals of different frequencies, a second source of two other course indicating signals of the same frequencies, one of the signals of said second source being. advanced in hase and the other being 90 delayed in phase with respect to the corresponding signals from said first source, a radio frequency source, means for supplying energy from said radio frequency source to both modulators of said pair, means for supplying energy from said first source to one of said modulators and from said second source to the other of said modulators, and means for coupling the output of said modulators to said radiating means, to supply carrier frequency energy from both said modulators in additive phase relation to said second antenna system and for supplying sideband energy from said both modulators to said first and second antenna systems, the phase relationship between the sideband energies from the two modulators in one of said systems being the same as at the output of said modulators, and the phase relationship between the sideband energies from said two modulators in the other of said systems being in phase opposition with respect to the output of said modulators.

13. A radio beacon comprising a first radiating means including a pair of spaced radiator elements, a centrally arranged radiating means, a pair of modulators, a first source of two course indicating signals of difierent frequencies, a second source of two other course indicating signals of the same frequencies, one of the signals of said second source being 90 advanced in phase and the other being 90 delayed in phase with respect to the corresponding signals from said first source, a radio frequency source, means for supplying energy from said radio frequency source to both modulators of said pair, means for supplying energy from said first source to one of said modulators and from said second source to the other of said modulators, and means for coupling the output of said modulators to said radiating means to supply carrier frequency energy from both said modulators in additive phase relation to said central radiating means, sideband energy from said two modulators in the same phase as at the output of said modulators to one of said radiating means, and to supply sideband energy from said two modulators in phase reversed relation with respect to the relation at the output of said modulators to the other of said radiating means.

14. A radio beacon according to claim 13 further comprising a source of voice frequency and means for supplying voice frequency energy from said source to both said modulators in such relation that the voice signal sideband energy from both said modulator will be supplied to said central radiating means in phase additive relation.

15. A radio beacon comprising a first radiating means including a pair of spaced radiator elements, a centrally arranged radiating means, a pair of modulators, a first source of two course indicating signals of different frequencies, a second source of two other course indicating signals of the same frequencies, one of the signals of said second source being 90 advanced in phase and the other being 90 delayed in phase with respect to the corresponding signals from said first source, a radio frequency source, means for supplying energy from said radio frequency source to both modulators of said pair, means for supplying energy from said first source to one of said modulators and from said second source to theother of said modulators, and means for coupling the output of said modulators to said radiating means to supply carrier frequency energy and sideband energy from said two modulators in the same phase relation as at the output of said modulators to said central radiating means and to supply sideband energy from said two modulators in phase reversed relation with respect to the phase relation at the output of said modulators to said pair of spaced radiating means.

16. A radio beacon according to claim 15 wherein said means for coupling comprises a. reentrant transmission line bridge circuit.

17. A radio beacon according to claim 15 further comprising a source of voice signals, means for supplying energy from said voice frequency source to said two modulators in such relation that said coupling means will serve to supply sideband energy from both said modulators to said central radiation means in additive phase.

ANDREW ALFORD. NATHAN MARCHAND. 

